An electric driving system of a hydraulic pressure pump and a wheel driver is developed, and AC motors are extensively used to accomplish higher efficiency than a DC motor. Of the AC motors, especially, an IPM motor has a high drive efficiency and also is excellent in responsibility. For this reason, the IPM motor has been extensively used in recent years. For control of the IPM motor, correct position data of a rotor is necessary, unlike the conventional DC motor and AC motor (induction motor).
The following position detecting devices are known as the conventional technique to obtain the position data of a rotor in a motor.
(a) Resolver and Encoder
The resolver to obtain position data and the encoder having a Z phase are expensive, and a kind of it is limited, and there is no fitting one depending on an axis diameter.
(b) Hall Element+Encoder Pulse to Obtain Position Data
Two sensing sections are necessary and input points for the Hall element increase.
(c) Low Resolution Pulse Encoder+Speed Estimation
Algorithm for estimating speed is incorporated to compensate the low resolution of the low resolution pulse encoder. Therefore, a calculation amount increases and practical use is difficult.
(d) Sensorless Control
A calculation amount is more, and practical use is difficult in point of responsibility and reliability.
A rotor position detection error by the position detecting device causes a torque error in the motor. As factors due to which the rotor position detection error is caused, there are:
(1) estimation error of a rotor initial position,
(2) lack of a pulse resolution,
(3) delay of detection in hardware and delay of speed calculation in software,
and so on.
In a conventional induction motor, an encoder and a bearing sensor were mainly used to acquire speed data. On the other hand, in the IPM motor, a resolver is mainly used to acquire correct position data but the resolver is expensive.
Therefore, it is demanded to realize AC motors such as the IPM motor in which the position control of the rotor can be carried out in a high precision while using a cheaper position detecting device, in order to realize an electric driving system of a hydraulic pressure pump and a wheel driver cheaply in high efficiency.
In conjunction with the above description, “Speed Control Device of Motor” is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 5-146188). In the first conventional speed control device of a motor, a speed detector sends out the detected speed of the motor as a pulse output. A speed estimation observer converts a load torque estimation observer of minimum dimension into a discrete model in a speed control period and a speed detection period and estimates speed in an interval between pulses outputted from the speed detector. Especially, in the speed estimation observer, a first calculating section calculates a model output estimation value by integrating a difference between a torque command and a load torque estimation value with respect to an observer model mechanical time constant. A second calculating section calculates an average of the model output estimation values outputted from the first calculating section in a pulse interval. A first difference section calculates deference between the output of the second calculating section and an average speed from a speed detector which is determined in case of the pulse change. An observer gain section calculates a load torque estimation value by multiplying the difference obtained by the first difference section by an observer gain. A second difference section calculates a difference between the model output estimation value from the first calculating section and the difference from the first difference section. A third difference section calculates a difference between the speed estimation value from the second difference section and a speed setting value. The difference calculated by the third difference section is supplied to a speed amplifier, and an adding section adds the output of the speed amplifier and the load torque estimation value of the observer gain section to acquire a torque command. In the speed control apparatus for a motor, a predicted velocity calculating section calculates a prediction speed for every speed control period until an output pulse is supplied from the speed detector. A comparator is supplied with the prediction speed calculated by the calculating section and the speed estimation value calculated by the second difference section. When the speed estimation value outputted from the second difference section is larger than the predicted speed, an ON output is sent out and when the predicted speed is equal to or larger than the speed estimation value, an OFF output is sent out. When the comparator outputs the ON output, a switch supplies the predicted speed to the third difference section, and when the comparator sends out the OFF output, the switch supplies the speed estimation value to the third difference section.
Also, “Rotation Position Detecting Apparatus of Rotation Machinery” is disclosed in the Japanese Laid Open Patent Application (JP-A-Heisei 8-54205). In the rotation position detecting apparatus of the rotation machine of this conventional example, a circular board is formed so as to repeat in a circumferential direction, one state for 180° and another state different from one state in electric angle alternately. The circular board is fixed to a rotation axis of the rotation machine. Three sensors are respectively arranged in positions which are distanced by 120° from each other in the mechanical angle in the circumferential direction. Thus, the one state and the other state are detected in accompany with the rotation of the circular board and a binary signal corresponding to the detected state is outputted from each of the sensors. The rotary encoder has the circular board coupled to this rotation axis to generate pulses for a number corresponding to the rotation angle when an interval between absolute positions is subdivided, and data indicative of a rotation direction of the rotation axis, and the sensor arranged closely to the circular board. The calculating section detects an absolute position of the rotation axis in units of 60° in the electric angle by a combination of the binary signals from the three sensors. Then, the calculating section processes the signal indicating this absolute position and the signal indicating a relative position between adjacent absolute positions which is an output signal of the sensor of the rotary encoder and calculates the rotation position of the rotation axis.
Also, “Rotation Detection Mechanism of Motor” is disclosed in Japanese Laid Open Patent application (JP-P2002-44910A). In this conventional example, the rotation detection mechanism is provided with a bearing sensor in which a sensor section for detecting the number of rotations of a motor and a bearing section for supporting a motor axis are integrated. The bearing sensor is mounted in the end cover of the motor with a plate member. The bearing section is engaged to a first concave section formed in the end cover of the motor and protrudes from the end cover inside. A second concave section is formed to be engaged with the angle of the bearing section which is prominent.
Also, “Electric Angle Detecting Apparatus and Driving Apparatus of Synchronous Motor” is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 9-238495). In this conventional example, the electric angle detecting apparatus for the synchronous motor, multi-phase current flows through windings and a rotor is rotated through interaction of the magnetic field by the windings and magnetic field of permanent magnets. A storage section previously stores a relation between the electric angle and current flowing through each of the multi-phase windings in accordance with a voltage when the voltage is applied for a combination of currents flowing through the multi-phase windings. A voltage applying section applies the voltage for the combination, and a detecting section detects each of the currents flowing through the multi-phase windings when the voltage is applied by the voltage applying section. An electric angle calculating section refers to the relation stored in the storage section based on the currents of the windings detected by the detecting section to determine an electric angle of the motor between 0° to 2π.
Also, “Lift Height Detecting Apparatus and Lift Track With the Same” is disclosed in Japanese Laid Open Patent Application (JP-P2004-018190A). In the lift height detecting apparatus of this conventional example, a rotation detecting section detects the number of rotations of rotatable up-and-down guidance roller provided for an up-and-down body. A movement quantity calculating section an up-and-down movement quantity of the up-and-down body through calculation based on the number of rotations of the up-and-down guidance roller. A lift height calculating section calculates a current height of the up-and-down body by summing the up-and-down movement quantity.